Angiotensin in brain has a variety of powerful physiological effects which have raised the question of the possible existance of an endogeneous renin-angiotensin system within the brain. We have demonstrated that a neutral-protease with properties of renal renin exists within the brain of dogs, and preliminary data suggests that the amount of this enzyme in brain is controlled differently from the amount of renin in plasma or kidney. In order to assess the physiological significance of this brain renin-like (iso-renin) enzyme, two initial steps must be taken. First, it must be purified to homogeneity to permit a careful comparison of this enzyme from brain to renin from the kidney. Second, a method of assay specific for this enzyme must be developed to permit the assay of reninlike (iso-renin) activity in brain under a variety of differing physiological states. It is proposed in this project to accomplish both of these preliminary steps.